Ok first off,
If you are getting into merchanting strictly to make money YOU WILL FAIL. Believe me I have tried to guide some friends in this and most of them end up becoming frustrated or impatient and usually lose money instead of earn money.
Basically, if you want to merchant or "powertrade" you gotta love it. If you have more fun farming ecto, I suggest you continue to do so.
On another note,
If you do want to pursue this, I suggest you find items that you like playing around with - whether it be minis, weapons, shields, consummables, tomes, whatever - and start watching prices on them in Kamadan for a week. Also look at price check threads and auctions. Be an active note-taker. Be friendly as you will have repeat customers and develop a good or bad reputation, or somewhere in the middle
Oh another thing, don't put all your eggs in one basket
AC